An electric motor-pump assembly is described in WO 2010/069963 A1, which is incorporated by reference. The crankshaft is configured as follows: The output shaft of the electric motor is of reduced cross section at its end projecting from the electric motor housing and thereby forms a bearing journal there, on which two or more eccentrics are arranged, rotationally locked.
The eye of a connecting rod is rotatably supported on each of the eccentrics. The connecting rod is in turn connected to the working element of the vacuum pump, which may be a piston or a working diaphragm. Each eccentric is moreover integrally provided with a balance weight. The rotationally locked connection of the eccentrics to the bearing journal is produced through a frictional grip. For this purpose the bearing journal is inserted through the openings in the eccentric. Since these openings have a somewhat smaller cross section than the bearing journal, a press-fit is created, which consists of a strong frictional grip between the circumferential face of the opening and the bearing journal.
In addition, three-dimensional position codings are provided on the eccentrics, which ensure that the two eccentrics and their balance weights are oriented in a predefined angular position relative to one another, so as to achieve the quietest possible running of the vacuum pump. For position coding, pins are situated on the one side of each eccentric and holes, which are intended to receive the pins, on the other side.
This makes the manufacture and assembly of the eccentrics an expensive process.